Method and Apparatus For Guiding Placement of Vehicle Service Fixtures

ABSTRACT

A machine vision system is configured to facilitate placement of a vehicle service apparatus relative to an associated vehicle. The machine vision system is configured to utilize images of optical targets received from one or more cameras to guide the placement of the vehicle service apparatus relative to the associated vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of, and claims priority from,U.S. patent application Ser. No. 10/646,644 filed on Aug. 22, 2003,which is herein incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates to the alignment of vehicle componentsrelative to one or more features of a vehicle, and in particular, tomethods and apparatus for adjusting the alignment of vehicle collisionavoidance systems with the travel direction of the vehicle using machinevision components.

Machine vision vehicle wheel alignment systems have been in use by thevehicle service industry for several years. A typical machine visionvehicle wheel alignment system, such as the Series 811 wheel alignmentsystem, configured with the DSP600 sensors manufactured by HunterEngineering Co. of Bridgeton, Mo. consists of a console unit, cameras,and optical targets. The console unit contains a computer configuredwith image processing and vehicle wheel alignment software applications,and incorporates various operator interfaces, including a keyboard, amouse, a printer, and a display device. The cameras are coupled to thecomputer, and the optical targets are disposed in the field of view ofthe cameras, typically mounted to the wheels of a vehicle undergoing analignment inspection.

Commonly, to view the left and right sides of a vehicle, two or morecameras are disposed on opposite sides of the vehicle, each having afield of view encompassing one or more wheels of the vehicle. Inalternative configurations, two cameras are provided on each side of thevehicle, each having a field of view encompassing a single vehiclewheel, i.e. a left front, left rear, right front, and right rear wheel,respectively. To facilitate vehicle wheel alignment, optical targets aremounted on the vehicle wheels, and observed by the cameras. The opticaltargets preferably have predetermined features which are identified inimages obtained by the cameras, and which facilitate a determination ofthe position and orientation of the optical targets. The imageprocessing may either take place in the camera modules, or in theconsole computer. Once the position and orientation of each opticaltarget is determined, the position and orientation of the associatedvehicle wheel can be determined, and corresponding, the various vehiclewheel alignment angle measurements may be either determined orcalculated. These angles typically include camber, caster, and toeangles for each vehicle wheel, the vehicle centerline, and the vehiclerear thrust line.

It is becoming increasingly common for automotive vehicles to beequipped with adaptive cruise control systems which includeforward-looking collision avoidance radar components. Collisionavoidance radar components, such as those manufactured by Robert BoschGmbH of Germany, typically operate in either a frequency modulation (FM)or continuous wave (CW) mode to transmit a signal from an antennatypically located in the front grill area of an automobile. Thecollision avoidance radar then determines from the return signalreceived by the antenna a distance an object causing the return signalis located from the automobile and the rate of closure of the object.Systems in the United States of America are currently configured tooperate within a 76-77 GHz frequency band allocated by the FederalCommunications Commission (FCC) for collision avoidance radar systems.However, other collision avoidance systems may be constructed whichoperate within different portions of the electromagnetic spectrum, forexample, utilizing infrared or visible light lasers to obtaininformation about objects in the path of a vehicle, or alternatively,utilizing ultrasonic signals.

To obtain an accurate measure of the distance between the vehicle onwhich the collision avoidance components are mounted and an object fromwhich emitted radar or laser signals are reflected, it is necessary toensure that the emitted signals are transmitted along the same vector asthe vehicle is traveling, which is typically the vehicle rear thrustline for straight-line motion. Any misalignment between the transmissionvector and the direction of vehicle travel may result inmisidentification of approaching objects, a miscalculation of thedistances between the vehicle and the object, and accordingly, amiscalculation of the rate of closure between the two. Depending uponthe severity of the miscalculation, the collision avoidance componentsmight fail to recognize an impending collision, or in the case ofadaptive cruise control systems, might signal a reduction in vehiclespeed which is less than that which is required to safely avoid acollision.

Conventionally, the manufacturer of the vehicle collision avoidancesystem provides a vehicle service apparatus specifically designed tofacilitate the alignment of the signal emitting and receivingcomponents. Examples of vehicle service apparatus designed to facilitatethe alignment of collision avoidance systems can be found in U.S. Pat.No. 6,363,619 B1 to Schrimer et al. and in U.S. Pat. No. 6,583,868 B1 toHopfenmuller. Typically, a collision avoidance system alignment fixtureis placed in front of the vehicle, and configured with components tofacilitate a precise placement relative to the vehicle. These mayinclude alignment marks onto which lasers are projected from vehiclemounted laser pointers, i.e., as shown in the '868 Hopfenmuller patent,or alignment mirrors as shown in the '619 Schrimer et al. patent.Alternatively, the collision avoidance system alignment fixture mayinclude mounting points for traditional transducer-based vehicle wheelalignment sensor heads. Preferably, these mounting points areperpendicularly disposed to a steer axis of the collision avoidancesystem alignment fixture, generally defined by as the centerline of thefixture. The mounting points are preferably spaced apart from thecollision avoidance system alignment fixture on extension arms, suchthat each is approximately disposed outward of the vehicle's sides tofacilitate reference to similar sensor heads attached to the vehiclewheels.

Once the vehicle wheels have been properly aligned, or the vehicle wheelalignment angles including the rear thrust line have been measured withthe traditional transducer based vehicle wheel alignment sensor heads,wheel alignment sensor heads are removed from the front wheels of thevehicle, and placed on the mounting points on the collision avoidancesystem alignment fixture. With the mounting points disposed outward ofthe vehicle's sides, the traditional transducer-based vehicle wheelalignment sensor heads removed from the front wheels may still cooperatewith the vehicle wheel alignment sensor units which remain mounted tothe rear wheels of the vehicle to determine a relative alignment betweenthe collision avoidance system alignment fixture and the vehicle rearthrust line.

Accordingly, it would be highly advantageous to facilitate the placementof alignment fixtures of a vehicle collision avoidance system relativeto the direction of travel of the associated vehicle, using componentsof a machine vision vehicle wheel alignment system, thereby eliminatingthe need for vehicle service centers to either delay acquiring machinevision vehicle wheel alignment systems or maintain both a machine visionvehicle wheel alignment system and a conventional transducer-basedvehicle wheel alignment system for purposes of aligning vehiclecollision avoidance systems.

It would be further highly advantageous in some applications tofacilitate the placement of a vehicle service apparatus, such as aheadlight aiming device or sensing devices for providing drivingassistance such as Intelligent Vehicle Highway Systems, relative to anassociated vehicle undergoing a vehicle service procedure usingcomponents of a machine vision vehicle wheel alignment system, therebyeliminating the need for additional or supplemental alignment equipmentor procedures.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, in a preferred embodiment, a machine vision vehiclewheel alignment system is operatively coupled with one or more camerasmounted to a vehicle service apparatus to facilitate placement of thevehicle service apparatus relative to an associated vehicle. The camerasare mounted to the vehicle service apparatus such that one or moreoptical targets mounted to the wheels of the associated vehicle are in acorresponding field of view. The vehicle wheel alignment system isconfigured to utilize data from images acquired by the cameras to guidethe placement of the vehicle service apparatus relative to theassociated vehicle.

In an alternate embodiment, a machine vision vehicle wheel alignmentsystem is configured to observe one or more optical targets mounted to avehicle service apparatus. The vehicle wheel alignment system isconfigured to utilize data from images of the optical targets on thevehicle service apparatus, in conjunction with images of optical targetsmounted to the vehicle wheels, to facilitate placement of the vehicleservice apparatus relative to the vehicle.

In an alternate embodiment, a machine vision vehicle wheel alignmentsystem is operatively coupled with one or more cameras mounted to acollision avoidance system alignment fixture to facilitate positioningof the collision avoidance system alignment fixture relative to the rearthrust line of an associated vehicle. The cameras are mounted to thecollision avoidance system alignment fixture such that one or moreoptical targets mounted to the rear wheels of the associated vehicle arein a corresponding field of view. The vehicle wheel alignment system isconfigured to utilize data from images acquired by the cameras to guidethe placement of the collision avoidance system alignment fixturerelative to the rear thrust line of the associated vehicle.

In an alternate embodiment, a machine vision vehicle wheel alignmentsystem is configured to observe one or more optical targets mounted to acollision avoidance system alignment fixture. The vehicle wheelalignment system is configured to utilize data from images of theoptical targets mounted to the fixture, in conjunction with images ofoptical targets mounted to the rear wheels of the associated vehicle, tofacilitate placement of the collision avoidance system alignment fixturerelative to the rear thrust line of an associated vehicle.

A method of the present invention for guiding the placement of a vehicleservice apparatus relative to an associated vehicle includes the stepsof mounting one or more optical targets on the associated vehicle andmounting one or more cameras on the vehicle service apparatus such thatthe optical targets are in the field of view of the one or more cameras.Images from the one or more cameras are processed to guide the placementof the vehicle service apparatus relative to the associated vehicle.

An alternate method of the present invention for guiding the placementof a vehicle service apparatus relative to an associated vehicleincludes the steps of mounting one or more optical targets on theassociated vehicle and one or more optical targets on the vehicleservice apparatus such that each of the optical targets is in the fieldof view of one or more cameras associated with an optical vehicle wheelalignment system. Images of the targets on the associated vehicle and onthe vehicle service apparatus acquired by the one or more cameras areprocessed to guide the placement of the vehicle service apparatusrelative to the associated vehicle.

In an alternate embodiment, machine vision components including camerasand optical targets are operatively coupled to a vehicle and to avehicle service apparatus to facilitate placement of the vehicle serviceapparatus relative to the vehicle. A positioning guidance system isconfigured to utilize data from images acquired by the cameras to guidethe placement of the vehicle service apparatus relative to theassociated vehicle.

The foregoing and other objects, features, and advantages of theinvention as well as presently preferred embodiments thereof will becomemore apparent from the reading of the following description inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the accompanying drawings which form part of the specification:

FIG. 1 is a block diagram of a prior art optical vehicle wheel alignmentsystem;

FIG. 2 is a simplified illustration of vehicle wheel alignment anglesand the placement of a vehicle service apparatus;

FIG. 3 is a perspective illustration of the placement of vehicle wheelalignment system cameras and vehicle service apparatus cameras relativeto optical targets disposed on the vehicle;

FIG. 4 is a perspective illustration of a portable camera unit having amounting shaft;

FIG. 5 is a perspective illustration of the placement of vehicle wheelalignment system cameras and optical targets disposed on the vehicle andon the vehicle service apparatus;

FIG. 6 is a perspective illustration of the placement of vehicle serviceapparatus cameras relative to optical targets disposed on the vehicle;

Corresponding reference numerals indicate corresponding parts throughoutthe several figures of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description illustrates the invention by way ofexample and not by way of limitation. The description clearly enablesone skilled in the art to make and use the invention, describes severalembodiments, adaptations, variations, alternatives, and uses of theinvention, including what is presently believed to be the best mode ofcarrying out the invention.

Turning to FIG. 1, the basic components of a conventional machine visionvehicle wheel alignment system, such as the Series 811 Aligner with theDSP600 sensors from Hunter Engineering Co. of Bridgeton, Mo. are showngenerally at 10. The system 10 is configured to determine the positionand orientation of vehicle wheels 11, 13, 15, and 17, and the axis aboutwhich they roll. Each vehicle wheel has associated therewith one or moreoptical targets 11A, 13A, 15A, and 17A. Optionally, additional opticaltargets may be associated other components of the vehicle, with a liftrack, or other support structure on which the vehicle wheels rest. Theimages of the optical targets are preferably obtained by four cameras21, 23, 25, and 27, with one camera associated with each wheel. Theoptical paths between the targets and the corresponding cameras areillustrated by the dashed lines in FIG. 1. Those of ordinary skill inthe art will recognize that the number of cameras may be varied,provided that images of each optical target are obtained and processedby the system.

The signals from the cameras are supplied to the wheel alignment systemconsole, and in particular, to a computer 31 disposed within theconsole. The computer is configured with software to utilize data fromthe acquired images to determine various wheel alignment angles. Theprocess of calculating the alignment angles may be done in many ways,such as shown in U.S. Pat. Nos. 5,488,472, 5,870,315, 5,675,515, and5,724,128, the disclosures of which are herein incorporated byreference. Correspondingly, methods and procedures for processing imagesof optical targets to establish coordinate reference systems, identifypositions and orientations within those systems, transform data betweenestablished coordinate reference systems, and to determine alignmentmeasurements are well known to those of ordinary skill in the art ofmachine vision vehicle wheel alignment, and are shown in U.S. Pat. No.6,064,750 to January et al., and U.S. Pat. No. 6,134,792 to January, thedisclosures of which are herein incorporated by reference.

Turning to FIG. 2, a vehicle service apparatus 100 which is to bepositioned relative to a vehicle is shown in front of a vehicle liftrack 102 consisting of left and right lift ramps upon which a vehicle isdisposed. The vehicle service apparatus 100 may consist of a housing104, and includes a pair of extension bars 106R and 106L which extendlaterally from the housing 104. The extension bars 106R and 106L have acommon lateral axis, and are fixed relative to the housing 104. Alongitudinal axis through the housing 104, referred to as the steeraxis, is perpendicular to the common lateral axis of the extension bars106R and 106L. Disposed at the outward ends of each of the extensionbars 106R and 106L are sockets 108, each configured to receive analignment component 110. Preferably, each alignment component 110 is acamera 112, however, in an alternate embodiment discussed below, eachalignment component 110 consists of an optical target 114 such asconventional optical targets 11A, 13A, 15A, or 17A. Correspondingalignment components 110, which may consist of either cameras 112 oroptical targets 114, depending upon the particular configuration of thevehicle service apparatus 100 as discussed below, are secured to thevehicle wheels as required to cooperate with the alignment components110 on the extension bars 106R, 106L.

Turning to a first embodiment of the present invention, shown in FIG. 3,cameras 112 are secured to the sockets 108 on each extension bar 106Rand 106L. Each camera 112 is positioned and oriented to have a field ofview which includes at least one optical target 114 secured to a vehiclewheel as required to carry out measurements of vehicle wheel alignment.Preferably, the camera 112 secured to the extension bar 106R on theright side of the vehicle is positioned and oriented such that thetarget 114 on the right rear wheel 15 of the vehicle is within the fieldof view of the camera. Correspondingly, the camera 112 secured to theextension bar 106L on the left side of the vehicle is positioned andoriented such that the target 114 on the left rear wheel 13 is withinthe field of view of the camera. Those of ordinary skill in the art willrecognize that removal of targets 114 from the front left and rightvehicle wheels 11 and 17 may be required to provide a clear field ofview of the targets 114 on the rear left and right wheels 13, 15 to thecameras 112.

Each camera 112 is operatively coupled to the computer 31 in the wheelalignment system console 30 using conventional communicationscomponents, such as a connecting cable capable of transmitting signals,or via wireless communications link. For example, each camera 112 mayutilize the same style cable and connector as the conventional wheelalignment cameras 21, 23, 25, and 27.

The computer 31 is configured with software to process the data receivedfrom each camera 112 to determine a spatial relationship between eachcamera 112 and an optical target 114 present in an associated field ofview. The computer 31 is further configured to utilize the determinedspatial relationships and data previously acquired from the cameras 21,23, 25, and 27 related to the position and orientation of the targets114 on each vehicle wheel, to guide the operator to adjust the placementof the vehicle service apparatus 100 to the manufacturer's recommendedposition and orientation relative to the vehicle. For example, theposition and orientation of the vehicle service apparatus 100 may bealigned such that the steer axis of the vehicle service apparatus 100,as defined by a line perpendicular to the common axis of the extensionbars 106R and 106L, is aligned with the rear thrust line of the vehicle(shown in FIG. 2). Generally, it is not required that the steer axis bealigned collinearly with the rear thrust line, so long as the steer axisand the rear thrust line are parallel.

For cameras 112 which are removable from the sockets 108, such as forattachment to other vehicle service apparatus, it is preferable that thecamera 112 have a fixed stub (mounting) shaft 116 secured to the body118, as seen in FIG. 4. Prior to use, it is necessary to determine therelationship between the fixed stub (mounting) shaft 116 axis ofrotation and the axis of the camera lens 120, i.e., the cameracoordinate reference system. One method for determining the directionvector of the shaft in the camera coordinate reference system is toposition an optical target 114 in the field of view of the camera.Images of the optical target 114 are acquired with the camera secured ina first rotational position about the fixed stub (mounting) shaft 116,and with the camera secured in a second rotation position about thefixed stub shaft. Using known mathematical transformations, such asdescribed in U.S. Pat. No. 5,724,128 to January, the position anddirection of the rotational axis of the camera about the fixed mountingshaft 116, relative to the coordinate system of the camera lens 120, canbe determined and stored for use as a calibration value.

In an alternate embodiment of the present invention shown in FIG. 5,each alignment component 110 secured to the extension arms 106R and 106Lis an optical target 114 instead of a camera 112. Each optical target114 on the extension arms 106R, 106L is disposed within the field ofview of at least one camera associated with the vehicle wheel alignmentsystem, such as cameras 21, 23, 25, or 27. These cameras may have widefields of view which encompass both the optical targets 114 mounted tothe vehicle wheels 11, 13, 15, 17, and the optical targets 114 mountedto the extension arms 106R, 106L or alternatively, may have fields ofview which are adjustable, such as through movement of the cameras toselectively view either the optical targets 114 mounted to the vehiclewheels 11, 13, 15, 17 or the optical target 114 secured to the extensionbars 106R, 106L. Alternatively, the vehicle wheel alignment system maybe configured with one or more additional cameras (not shown) orientedto view the approximate location of each of the optical targets 114secured to the extension bars 106R, 106L. The wheel alignment computer31 is configured with software to process the data received from thecameras viewing each of the optical targets 114, to determine a spatialrelationship between each optical target 114, i.e., between the vehicleand the vehicle service apparatus 100.

The number of optical targets 114 required to align the vehicle serviceapparatus 100 is dependent upon several factors, including the desiredaccuracy with which the vehicle service apparatus 100 is to be aligned,and the quality of the apparatus itself, such as the extension bars106R, 106L and sockets 108 used to attached the optical targets 114 tothe vehicle service apparatus 100. For example, for collision avoidancesystem applications, the vehicle service apparatus manufacturers mayprovide precisely machined sockets 108 which have a fixed and knownrelationship (typically normal) to the housing 104 of the vehicleservice apparatus 100. For these applications, only one optical target114 is required, because the relationship between the target mounting inthe socket 108 and the housing 104 is known. Alternatively, if thesockets 108 are not precisely machined, or are not in a knownrelationship to the housing 104, two optical targets 114 are utilized todefine a steer axis for the vehicle service apparatus 100 which may bealigned relative to one or more vehicle wheel alignment angles. Those ofordinary skill in the art will recognize that it may be necessary torotate the optical targets 114 within the sockets 108 to two or morepositions, and to acquire images of the optical targets 114 in eachrotational position, thereby acquiring sufficient information toidentify an axis of rotation of the optical targets, andcorrespondingly, an axis of the extension bar 106R or 106L.

The wheel alignment computer 31 is configured to utilize the determinedspatial relationships and data previously acquired from the cameras 21,23, 25, and 27 related to the position and orientation of the opticaltargets 114, to guide the operator to adjust the current position andorientation of the vehicle service apparatus 100 to the manufacturer'srecommended placement. For example, the position and orientation of thevehicle service apparatus 100 may be adjusted such that a steer axis ofthe vehicle service apparatus 100 is parallel with the rear thrust lineof the vehicle. Alternatively, those of ordinary skill in the art willrecognize that it is functionally equivalent to first determine arelationship between the vehicle front and rear thrust lines, and tothen adjust the position of the vehicle service apparatus 100 relativeto the front thrust line of the vehicle, compensating for any front torear variation. This assumes that the position and orientation of thefront wheels is not changed after the relationship to the rear thrustline is determined.

As a method for aligning a vehicle service apparatus 100 relative to avehicle, the present invention requires that an operator initiallyutilize a machine vision vehicle wheel alignment system in aconventional manner to acquire one or more alignment measurementsassociated with the vehicle. Typically, conventional operation of amachine vision vehicle wheel alignment system requires that a set ofoptical targets 114 be mounted to the vehicle wheels 11, 13, 15, and 17.Images of the optical targets are then acquired by one or more cameras21, 23, 25, and 27 and processed to obtain measurements of theassociated wheel alignment angles for the vehicle. When positioning avehicle service apparatus 100, such as a radar alignment fixture, thevehicle service apparatus 100 must be aligned to the direction of travelfor the vehicle, accordingly, it is necessary to obtain a measurement ofthe vehicle rear thrust line, which is representative of the directionof travel for the vehicle.

Once the vehicle wheel alignment measurements have been completed, theoperator initiates the alignment of the vehicle service apparatus 100,preferably by selecting a software option presented by the vehicle wheelalignment computer 31. Upon initiation of the vehicle service apparatusalignment, the computer 31 preferably computes the necessary vehiclewheel alignment angles and reference points in a three dimensionalcoordinate system defined by one of the optical targets 114 mounted tothe vehicle rear wheels 13, 15. The computer 31 further computes arepresentation of the relationship between each of the optical targets114. While the remaining steps of the method are described in thecontext of utilizing optical targets 114 secured to the rear wheels 13,15 of a vehicle, those of ordinary skill in the art will recognize thatif the vehicle service apparatus 100 is to be placed relative to thefront thrust line of the vehicle, after a vehicle alignment has beencompleted, the computer 31 will utilize the optical targets 114 securedto the front wheels 11, 17 and associated measurements or compensationvalues.

Next, the operator is instructed to remove optical targets 114 from thefront vehicle wheels 11 and 17, if required to provide a clear field ofview to the optical targets 114 on the rear wheels 13, 15, and to mountcameras 112 to the extension bars 106R and 106L of the vehicle serviceapparatus 100. The vehicle service apparatus 100 is positioned in frontof the vehicle, at approximately the vehicle centerline, such that theoptical targets 114 on the rear vehicle wheels 13, 15 are each withinthe field of a camera 112. The position and orientation of the cameras112 is locked, and the cameras 112 are operatively connected to thecomputer 31 using a conventional connector such as a communicationscable or wireless communications link.

Images acquired from each camera 112 of the optical targets 114 securedto the rear wheels 13, 15 are compared with the previously computedtarget relationships and wheel alignment angles to determine theposition and orientation of the vehicle service apparatus 100 in acommon coordinate system. Preferably, a common axis between the twocameras 112 is established perpendicular to a steer axis for the vehicleservice apparatus 100. Once the position and orientation of the vehicleservice apparatus 100 is identified, the computer 31 provides theoperator with instructions for adjusting the position and orientation ofthe vehicle service apparatus 100 such that the steer axis or otherfeature of the vehicle service apparatus 100 is aligned or positionedrelative to a predetermined vehicle wheel alignment angle or othermeasurement, such as the rear wheel thrust line.

Those of ordinary skill in the art will recognize that the instructionsmay be provided in numerical format, or may be provided visually, suchas through a “live” bar graph representative of the amount of movementrequired to position the vehicle service apparatus 100 in the desiredlocation. With the vehicle service apparatus 100 disposed at the desiredposition and orientation relative to the vehicle, the operator canconduct further necessary vehicle services, such as the alignment of aradar collision avoidance unit, in the conventional manner.

Turning to FIG. 6, an alternate method of the present invention foraligning a vehicle service apparatus 100 relative to the rear thrustline of a vehicle does not require that a machine vision system acquiremeasurements of actual vehicle wheel alignment angles prior to thepositioning of the vehicle service apparatus, and does not require thata common coordinate system be established between the left and rightsides of the vehicle. Conventionally, a vehicle rear thrust angle isdefined as (Left Rear Toe−Right Rear Toe)÷2. Correspondingly, a vehiclefront thrust angle is defined as (Left Front Toe−Right Front Toe)÷2.Substituting in the equations set forth above, it can be shown that forthe rear thrust angle and a front thrust angle to be equal, thefollowing condition must be satisfied: (Left Rear Toe÷Left FrontToe)=(Right Rear Toe−Right Front Toe). In summary, if the differencebetween the front and rear toe angles on each side of the vehicle isequal, the front and rear thrust lines are aligned with respect to eachother.

A vehicle service apparatus is aligned with respect to the rear thrustline of a vehicle when the steer axis of the vehicle service apparatus100 and the rear thrust line are the same or parallel, i.e. when theangle of the rear thrust line minus the angle for the steer axis=0.Since the vehicle service apparatus steer axis can be treated as anequivalent to a front thrust line, it becomes apparent that the vehicleservice apparatus 100 may be aligned with respect to the rear thrustline of the vehicle by comparing the angular variation between the leftrear wheel rotation axis of the vehicle and the left side of the vehicleservice apparatus 100 with the right rear wheel rotational axis of thevehicle and the right side of the vehicle service apparatus. Comparisonof the left and right rear wheel rotational axis with the left and rightsides of the vehicle service apparatus 100, such as represented by leftand right camera mounting shaft axes of rotation, does not need to beconducted in a common coordinate system or reference frame.

Accordingly, an alternate method of the present invention utilizes theangular relationships between the left and right sides of the vehicle toalign the vehicle service apparatus 100 relative to the rear thrust lineof the vehicle. First a pair of optical targets 114 are mounted to therear wheels 13, 15 of the vehicle. Next, a pair of cameras 112 aresecured to the extension bars 106R and 106L of the vehicle serviceapparatus 100, and are positioned such that the optical targets 114 areeach within the field of view of a respective camera 112. As previouslydescribed, the cameras 112 are each operatively coupled to a vehiclewheel alignment system computer 31, or to another suitable imageprocessing system i.e., a position guidance system, which may beindependent of a vehicle wheel alignment system. Improved accuracy canbe achieved with a bubble level or other suitable sensor or method isprovided to assist in alignment of the cameras 112 such that the opticalaxis (z-axis) of each camera 112 is parallel to the ground or surfaceupon which the vehicle is disposed.

The steps of this method assume that the steer axis of the vehicleservice apparatus 100 is the angle bisector of the mounting shaft axisfor each camera 112, or that any misalignment of the steer axis relativeto the mounting sockets 108 on the left and right sides of the vehicleservice apparatus 100 has been determined in a conventional manner andsuitable compensation or calibration calculations performed, such asdescribed in U.S. Pat. No. 5,724,128 to January.

With the cameras 112 aligned, the images of the associated opticaltargets are acquired and processed in a conventional manner, includingtarget compensation if required, to identify an axis of rotation foreach wheel of the vehicle on which the targets are secured. Preferably,the axis of rotation identified for the left rear wheel is compared withthe mounting shaft axis of the left side camera in the left side cameracoordinate system. Similarly, the axis of rotation for the right rearwheel is compared with the mounting shaft axis of the right side camerain the right side camera coordinate system. The position and orientationof the vehicle service apparatus 100 is then adjusted until the angledifferences between the wheel axis of rotation and the camera mountingshafts on each side are equivalent, at which point the vehicle serviceapparatus 100 is aligned relative to the rear thrust line of thevehicle.

In an alternate method of the present invention, the initial steps areidentical to those set forth above, however, optical targets 114 aredisposed on the extension arms 106R and 106L of the vehicle serviceapparatus 100 in place of the cameras 112. The vehicle service apparatus100 and optical targets 114 are positioned in front of, andapproximately in the center of, the vehicle such that each opticaltargets 114 is within the field of view of at least one cameraoperatively coupled to the vehicle wheel alignment system 10.

Images acquired of the optical targets 114 are compared with thepreviously computed target relationships and wheel alignment angles todetermine the position and orientation of the vehicle service apparatus100 in a common coordinate system. Preferably, a common axis between thetwo optical targets 114 is established perpendicular to a steer axis forthe vehicle service apparatus 100. Once the position and orientation ofthe vehicle service apparatus 100 is identified, the computer 31provides the operator with instructions for adjusting the position andorientation of the vehicle service apparatus 100 such that the steeraxis is aligned relative to a predetermined vehicle wheel alignmentangle or other measurement, such as the rear axle thrust line.

Those of ordinary skill in the art will recognize that the instructionsmay be provided in numerical format, or may be provided visually, suchas through a “live” bar graph representative of the amount of movementrequired to position the vehicle service apparatus 100 in the desiredlocation, such as shown in U.S. Reissue Pat. No. 33,144 to Hunter etal., which is herein incorporated by reference. With the vehicle serviceapparatus 100 disposed at the desired position and orientation relativeto the vehicle, the operator can conduct further necessary vehicleservices, such as the alignment of vehicle mounted radar collisionavoidance components, in the conventional manner.

Those of ordinary skill in the art will further recognize that theselection of the placement locations for the cameras and optical targetsmay be interchanged within the scope of the present invention so long asa positional relationship between the vehicle service apparatus 100 andthe vehicle can be determined. For example, it is considered within thescope of the present invention to mount forward-looking cameras on therear vehicle wheels, and to obtain images of optical targets disposed ona vehicle service apparatus 100 in front of the vehicle. Images acquiredby these cameras can be processed to determine a positional relationshipbetween a computed vehicle rear thrust line and the vehicle serviceapparatus 100.

The present invention can be embodied in part in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. The present invention can also be embodied in part in theform of computer program code containing instructions embodied intangible media, such as floppy diskettes, CD-ROMs, hard drives, or another computer readable storage medium, wherein, when the computerprogram code is loaded into, and executed by, an electronic device suchas a computer, micro-processor or logic circuit, the device becomes anapparatus for practicing the invention.

The present invention can also be embodied in part in the form ofcomputer program code, for example, whether stored in a storage medium,loaded into and/or executed by a computer, or transmitted over sometransmission medium, such as over electrical wiring or cabling, throughfiber optics, or via electromagnetic radiation, wherein, when thecomputer program code is loaded into and executed by a computer, thecomputer becomes an apparatus for practicing the invention. Whenimplemented in a general-purpose microprocessor, the computer programcode segments configure the microprocessor to create specific logiccircuits.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results are obtained. Asvarious changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A method for aligning a vehicle service apparatus relative to an associated vehicle, the vehicle service apparatus having a steer axis and a pair of lateral extension arms, a camera disposed on each of the lateral extension arms, comprising the steps of: mounting a first optical target on a first side of the associated vehicle in a field of view of a first of the cameras; mounting a second optical target on a second side of the associated vehicle in a field of view of a second of the cameras; acquiring one or more images of said first optical target with the first camera; acquiring one or more images of said second optical target with the second camera; identifying at least one vehicle measurement from said images acquired with the first camera; identifying at least one vehicle measurement from said images acquired with the second camera; and guiding the placement of the vehicle service apparatus relative to the associated vehicle utilizing said measurements.
 2. The method of claim 1 for aligning a vehicle service apparatus relative to an associated vehicle wherein said first and second optical targets are mounted on opposite rear wheels of the vehicle, respectively.
 3. The method of claim 1 for aligning a vehicle service apparatus relative to an associated vehicle wherein the step of identifying a plurality of vehicle measurements includes identifying a left wheel rotation axis and a right wheel rotation axis.
 4. The method of claim 3 for aligning a vehicle service apparatus relative to an associated vehicle wherein said left rear wheel rotation axis is identified in a first camera coordinate system, and wherein said right rear wheel rotation axis is identified in a second camera coordinate system.
 5. The method of claim 1 for aligning a vehicle service apparatus relative to an associated vehicle further including the steps of identifying, for each camera, a mounting axis; and evaluating said first camera mounting axis relative to said vehicle utilizing said at least one vehicle measurement identified from an image acquired by said first camera; evaluating said second camera mounting axis relative to said vehicle utilizing said at least one vehicle measurement identified from an image acquired by said second camera; and wherein said step of guiding the placement of the vehicle service apparatus relative to the associated vehicle includes guiding positional placement of the vehicle service apparatus until said first and second camera mounting axis are symmetrically disposed relative to the vehicle to within a predetermined tolerance of each other.
 6. The method of claim 5 for aligning a vehicle service apparatus relative to an associated vehicle further including the step of compensating for misalignment between said mounting axis of said first camera and said mounting axis of said second camera.
 7. An improved vehicle service apparatus having a housing configured for placement relative to an associated vehicle, the improvement comprising: a first camera coupled to the housing and having a first field of view including a first side of the associated vehicle; a second camera coupled to the housing and having a second field of view including a second side of the associated vehicle, said second side opposite said first side; a first optical target configured for attachment to the associated vehicle in said first field of view; a second optical target configured for attachment to the associated vehicle in said second field of view; and a computer configured to receive data from said first and second cameras and to guide the placement of the housing relative to the associated vehicle utilizing said received data.
 8. The improved vehicle service apparatus of claim 7 wherein the housing has a steer axis, and the associated vehicle has a thrust line; and wherein said computer is configured to guide the placement of the housing such that said steer axis of the housing is aligned parallel to said thrust line of the associated vehicle.
 9. The improved vehicle service apparatus of claim 7 further including: a left lateral extension arm fixedly secured to said housing; a right lateral extension arm fixedly secured to said housing on an opposite side from said left lateral extension arm; wherein said first camera is coupled to said left lateral extension arm; and wherein said second camera is coupled to said right lateral extension arm.
 10. The improved vehicle service apparatus of claim 9 wherein said computer is further configured to compensate for misalignment between said left lateral extension arm and said right lateral extension arm.
 11. A method for guiding placement of a vehicle service apparatus relative to an associated vehicle, comprising the steps of: positioning a first camera and a first optical target to operatively determine a relationship between a component on a first side of the vehicle and the vehicle service apparatus; positioning a second camera and a second optical target to operatively determine a relationship between a component on a second side of the vehicle and the vehicle service apparatus, said second side on an opposite side of the vehicle from said first side; acquiring one or more images of said first optical target with the first camera; acquiring one or more images of said second optical target with the second camera; determining at least a first vehicle measurement from said images acquired with the first camera; determining at least a second vehicle measurement from said images acquired with the second camera; guiding the placement of the vehicle service apparatus relative to the associated vehicle utilizing said first and second measurements.
 12. The method of claim 11 for guiding the placement of a vehicle service apparatus relative to an associated vehicle wherein said at least one vehicle measurement in said images acquired with the first and second cameras is determined relative to the vehicle service apparatus.
 13. The method of claim 11 for guiding the placement of a vehicle service apparatus relative to an associated vehicle further including the step of compensating for misalignment between a mounting axis of said first camera and a mounting axis of said second camera. 